(A) Field of the Invention
The present invention is related to an axial leaded over-current protection device, more specifically, to an axial leaded over-current protection device of a positive temperature coefficient (PTC).
(B) Description of the Related Art
The resistance of a positive temperature coefficient (PTC) conductive material is sensitive to temperature variation and can be kept extremely low during normal operation so that the circuit can operate normally. However, if an over-current or an over-temperature event occurs, the resistance will immediately increase to a high resistance state (e.g., above 104 ohm.) Therefore, the over-current will be eliminated and the objective to protect the circuit device will be achieved. Consequently, PTC devices have been commonly integrated into various circuitries so as to prevent the damage caused by over-current.
FIG. 1(a) illustrates a perspective diagram of a known over-current protection device 10. Two terminal metal strips 11 are respectively soldered to the upper and lower surfaces of a PTC element 12 and are used as connection interfaces to the appliance to be protected. FIG. 1(b) is the side view of the over-current protection device 10. The PTC element 12 is composed of two electrode layers 121 and a PTC material layer 122 laminated therebetween, and the two terminal metal strips 11 are respectively connected to the two electrode layer 121.
An over-current protection device is usually expected to lower its initial resistance as far as possible, so as to be used in low resistance applications. However, the area of the PTC element would increase when it is attempting to lower the resistance. Therefore, the over-current protection device is unsuitable for being used in small appliances as a result of the dimension increase of the over-current protection device.